Showing posts with label Titan. Show all posts
Showing posts with label Titan. Show all posts

Friday, November 19, 2010

Titan Aerial Explorer Proposal

Jonathan Lunine at the University of Arizona has just posted his intent to develop a proposal for a Titan Aerial Explorer.  From his announcement, "The mission to be proposed includes a balloon with the capability for ground-penetrating radar, radio science and multi-spectral imaging and spectroscopy, aerosol analyses, and possibly other instruments. The goal is to explore the processes that are at work on the surface on and near-surface of Titan with sufficient resolution and wavelength capability to quantify Titan’s methane hydrologic cycle."  The proposal would be submitted for the European Space Agency's next Medium class science mission for launch around 2022.

Editorial Thoughts: I would like to see one or more Titan in-situ missions fly in the 2020's.  Titan's thick atmosphere and low gravity makes it an easy world (once you spend many years flying there) to land on, float above, or fly around.  Lunine's mission potentially would face several challenges such as power (ESA currently does not have plutonium power sources, which as I understand it would be necessary both for power and to heat the gases for the balloon) and bringing the balloon technology up to flight readiness (the Titan Flagship mission's balloon reportedly was judged to require further technology development before flight).  However, Dr. Lunine has a solid resume, so he must have ideas on how to address these problems.

Monday, October 11, 2010

Titan Lake Probe Mission Concepts


Note: We appear to be in a quiet time for planning future planetary missions.  In the U.S., we are awaiting the recommendations of the Decadal Survey to be released next March.  In Europe, we are waiting for the decision for the next large mission selection between a Jupiter Ganymede orbiter and two astronomy missions.  I will post as information and ideas become available, but I expect that posts may occur every week or so for awhile.

One of the most exciting concepts for a future planetary mission has been a mission to land on and sample one of the large lakes of Titan.  The lakes are likely to be chemical repositories that contained important clues to Titan's "are repositories, through dissolution of airborne solids, of organics scattered globally on Titan, as well as noble gases, which are a key clue to Titan’s origin and evolution." Sampling the lakes will help answer important questions about Titan:

Cassini-Huygens leaves us with many questions that require a future mission to answer.  These include whether methane is out-gassing from the interior or ice crust today, whether the lakes are fed primarily by rain or underground methane-ethane aquifers (more properly, “alkanofers”), how often heavy methane rains come to the equatorial region, whether Titan’s surface supported vaster seas of methane in the past, and whether complex self organizing chemical systems have come and gone in the water volcanism, or even exist in exotic form today in the high latitude lakes." [NASA/ESA JOINT SUMMARY TITAN SATURN SYSTEM MISSION, January 2009]

As part of its analysis of missions to recommend in the coming decade, the Decadal Survey commissioned a study of possible Titan lake probe missions.  The results of the analysis was presented at a recent conference, and the studies' lead, John Elliott of JPL was kind enough to send me a copy of the presentation and answer some questions.

The study looked at addressing four key scientific questions using variations of two variations of probes that would sample one of Titan's large northern lakes.  The scientific questions were:

  • SGa: Atmospheric evolution (studied during descent through the atmosphere and by analyzing the lake)
  • SGb: Lake and atmospheric interaction to determine how the two exchange material much as the Earth's hydrosphere and atmsphere influence each other (studied by a long-lived floater on the surface of a lake)
  • SGc: Lake chemistry (studied by either a floater or a submersible)
  • SGd: Interior structure (studied by a long-lived submersible on the lake bottom to determine whether or not there is a large ocean deep beneath the surface as there is at Ganymede and Europa)

The study looked at a Flagship class (multiple billions of dollars) and three New Frontiers class (~$650M) missions.  Only the Flagship class mission would be able to address all questions.  It would place a long lived, plutonium-powered (via ASRGs) floater on the lake surface to study long term interactions and would deploy a submersible to the lake bottom for a thirty day stay before popping to the surface for data relay.  The presence of an interior ocean would be explored by measuring the depth of the lake from the lake bottom using an echo sounder.  The amplitude and phases of the lake tides would be used to infer the presence of an interior ocean.

The three New Frontiers missions would conduct subsets of the Flagship mission:

  • Long lived floater (ASRG powered) to study atmospheric evolution, lake/atmospheric interaction, and lake chemistry.  Communications would be direct to Earth and the carrier craft would be a simple stage attached to the entry shell, much like the carrier craft for NASA's Martian landers. 
  • A battery-powered submersible to study atmospheric evolution and lake chemistry.  The submersible would remain on the lake bottom for only six hours before returning to the surface to relay its data back to the carrier stage for retransmission to Earth.  (The presentation notes that this option would provide the most science for the dollar.)
  • A battery-powered floater that would survive on the lake surface for twelve hours to study atmospheric evolution and lake chemistry.  (The presentation notes that this would be the cheapest option.)

In addition to options for the lake probe, the mission also had multiple options for arriving at Titan and for relaying data.  One option would be to arrive at Titan by 2026 to enable direct transmission of data to Earth.   This option requires launch by 2020, and to achieve this short (for a Saturn mission) transit, the carrier would require substantial fuel to enable two deep space maneuvers.  A second option would be two launch by 2023 and arrive by 2032.  In this latter case, data relay would have to be through the carrier, which the study assumes would be ASRG powered.  (Elliot told me that solar powered carriers might be an option, but, "but there are a lot of unknowns (e.g. required technology developments) and uncertainties in how much array area we’d need and how well cells would perform at Saturn distances, etc., so we chose for the study to assume ASRGs as the simpler implementation given our current understanding.  This is something that could benefit from a more detailed trade if further studies are performed.")

The TIME Discovery proposal that is been discussed in this blog would most resemble the long-lived floater concept with direct communication to Earth and a dumb carrier.  The TIME mission assumes a launch by the mid portion of this decade, possibly eliminating the need for powered deep space maneuvers.  The Discovery proposal also would benefit from NASA providing the ASRG's outside the mission's PI budget of ~$450M, enabling the mission to potentially fit within that lower budget instead of a New Frontier budget (~$650M).

See Titan Mare Explorer (TiME) and Dive, Dive! Titan Submersible for additional background information.

Tuesday, October 5, 2010

High Resolution Imaging of Titan

Cassini VIMS maps of Titan from http://wwwvims.lpl.arizona.edu/

Mapping the surface of Titan is hard.  The smoggy atmosphere scatters most wavelengths of light.  The depth of the atmosphere prevents spacecraft from getting close enough for high resolution images.  Radar offers an alternative to optical imaging, but the equipment necessary is heavy, power hungry, and produces large amounts of data that must be transmitted back to Earth.  Resolution can also be a problem.  The Cassini radar system, which uses the spacecraft's large main antenna, has a maximum resolution of 350 m at closest approach.  The Huygen's landing area with its networks of hills and channels is a bright blur at these resolutions.

A recent presentation at the EPSC2010 conference, offers an alternative.  The Cassini VIMS instrument discovered a clear window in Titan's atmosphere at 5 microns, which is in the infrared region of the spectrum.  The authors propose a camera that would utilize that window to image Titan.  From a spacecraft flying by Titan, 100 images covering 1.25% of the surface could be taken.  Best resolution would be less than 50 m as the spacecraft swoops below ~2300 km above the surface during closest approach. That would provide sufficient detail to study the surface geomorphology in detail.  The channels at the Huygen's landing site, for example, would be seen.  (Cassini's infrared instrument, VIMS, was not optimized for spatial mapping and produces images with a maximum resolution of ~1 km.)

The lead author on the EPSC2010 abstract, Chrstophe Sotin of JPL, is also lead author of an abstract for the upcoming Division of Planetary Studies conference.  The second abstract provides a brief description of the goals for a conceptual mission called JET, a Journey to Enceladus and Titan.  The goals listed are high mass resolution spectroscopy of the material in Enceladus' geysers and Titan upper atmosphere to determine composition, high resolution thermal mapping of the Enceladus' tiger stripes that are the source of the geysers, and imaging of Titan's surface (presumably with the camera described above).

Editorial Thoughts: The proposed Flagship Titan orbiter would have used the 5 micron band to map the entire moon at resolutions of around 50 m.  The abstract summarized above made it clear that the authors are proposing their instrument for a spacecraft that would flyby Titan, presumably while in orbit around Saturn.  The area covered in detail at closest approach would be approximately one million square kilometers, a respectable area.  (France is 547,030 sq. km.)  It's not clear from the abstract how much of that area would be imaged at resolutions of 50 m or less.  By carefully choosing the areas to be imaged to include high priority sites, such an imager should make key contributions to our understanding of Titan's surface and the processes creating it.  While the authors don't discuss it, the imager should be able to image additional areas of Titan at lower resolutions from greater distances.

The imager that had been proposed for the Titan Flagship mission would have been more capable than the camera discussed here.  It too would have imaged the surface at 50 m resolution, but would have used an additional transparent band in the atmosphere to provide color images (at 2.0, 2.7, and 5 μm) that could provide compositional information.  The Flagship instrument also would have provided spectroscopy in the 0.85 –2.4 μm and 4.8–5.8 μm bands at 250 m resolution.  (The lower wavelengths, however, would have been subjected to greater scattering by Titan's atmosphere, reducing resolution.  The 5 micron band would provide the clearest images.)

I am hoping that the Decadal Survey prioritizes a New Frontiers class-Saturn orbiter to study Enceladus and Titan in the coming decade.  Such a mission could carry a small suite of instruments optimized to studying these bodies.  At Titan, a capable mass spectrometer could study the composition of the upper atmosphere while ice penetrating radar could study the near subsurface structure.  (The JET abstract does not mention an ice penetrating radar.)  Both instruments would also be essential for Enceladus studies.  The 5 micron camera presented here might be a Titan-specific instrument, although this could be a channel on a high resolution thermal imager.  The abstract authors don't present any information on their instrument's mass and cost.  The Flagship instrument, however, had a proposed mass of 28 kg, which suggests an instrument that may have costs and mass incompatible with a New Frontiers class mission.  Presumably, this is the reason that the authors of this abstract are proposing a simpler instrument focused only on imaging in one band.  (I use remote sensing in my research; it would be great if this type of instrument could also image in additional wavelengths.  Color images are a great tool for exploring composition with carefully selected wavelengths (as the Landsat imagers demonstrate for Earth studies).)  However, even images in one band would present a big step forward in our ability to study Titan.

Links:


Friday, July 2, 2010

Some Planetary Exploration Challenges

Some of the most interesting places in the solar system unfortunately present some daunting challenges to explore.  The intense radiation fields at Europa are probably the quintessential example of this problem.  With a decade of technology development to push radiation hardened engineering and a $3B+ budget, the proposed Jupiter Europa Orbiter will survive for an estimated 9 months or so after it enters orbit.  With that short of a lifetime and a whole world to explore, a fairly small percentage will be imaged at high resolution.  Eventual lander missions (if the findings of the orbiter warrant what would likely be a Flagship class mission) will be equally time pressed.

The hellishly hot surface of Venus provides its own challenge.  Landers and probes have lasted on the surface for an hour or so in the past.  The next generations of landers under consideration by NASA are targeting landed or near surface lifetimes of two-five hours.  These landers extend their life by including phase change materials within the landers.  Much as the ice in your ice chest does, these materials absorb heat as they change from solid to liquid.  Once the phase change is complete, however, the interior of the lander's temperature will rise as heat soaks through the shell.  The lead author of the Venus Mobile Explorer, Lori Glaze at the Goddard Spaceflight Center, explained to me in an e-mail the challenges faced by designers of Venus landers.  "The real challenge here is that if you want to keep the lander 'cool' you have to provide more phase change material, which has mass...At some point, you just can’t get this massive system off the ground at Earth."  As a result, Venus landers seemed destined to have just a few hours to perform their studies.  Long term studies can be done from balloons and orbiters, but long-term surface missions are beyond our capabilities.  (In theory, refrigeration units powered by plutonium 238 could resolve this problem.  However, these systems operate based on the difference in heat between the  plutonium and a thermocouple.  It's hard to "dump" the heat of the Pu-238 into an already hellish hot atmosphere to maintain the temperature difference.)

Titan has neither radiation fields nor heat to deal with.  It's atmosphere and surface are hellishly cold, but nuclear power systems do operate well in cold environments (easy to maintain that heat differnce).  This is a world that has a surface that in many ways may be most Earth-like of any body in the solar system with river valleys, seas and lakes, mountains, and a host of other interesting terrains.  Titan deserves the high resolution imagery that has advanced our understanding of the other Earth-like surface, Mars.  Unfortunately, the atmosphere of Titan and the dim light so far from the sun makes high resolution imaging from orbit almost impossible.  At Mars, orbiters can operate at 150 km altitude, while the atmosphere of Titan requires an altitude of 1500 km.  To see through the haze in a spectral window, a camera has to operate in near infrared bands.  The sun is dimmer at these wavelengths than at visible wavelengths and Saturn is far from the sun.  So to collect enough light to illuminate each pixel sufficiently for a clean image, a large mirror would be needed for high resolution imaging.  As a result of these limitations, the proposed Titan Flagship orbiter would have imaged the surface at 50 m per pixel where Mars is imaged at 30 cm per pixel.  (Radar instruments would have their resolution degraded by the increased altitude compared to what could be done at Venus or Mars.)  In addition, either optical or radar imaging system generate lots of data, which from the distance of Saturn require high powered communications systems.  High power communications systems require large power systems (and likely lots of Pu-238) leading to a large spacecraft.  Net result is that global, moderate resolution (~50 m) mapping of Titan may require a small Flagship-class (($1.5-2.0B?) missions.  In the meantime, in situ probes like the proposed TIME lake lander and the AVIATR plane offer ways to increase our knowledge of Titan at much more moderate costs.

Wednesday, June 16, 2010

AVIATR Titan Plane Details

Click on image to go to site for full poster plus additional posters.

A previous post looked at the proposed AVIATR Titan plane proposal.  This mission, which is currently contending for the next Discovery mission slot, would use an airplane to study the surface and atmosphere of Titan.  Unlike previously proposed balloon missions that would drift with the winds, this mission would be able to send the plane to survey specific surface targets such as river systems, lakes, and mountains.  The plane would be able to fly faster than Titan rotates, so that it would always remain on the sunlit, Earth-facing side of Titan.

A video of a presentation on the mission from a meeting last January has been posted on the web.  Together with a recently posted meeting abstract, more information on the science of the mission is now available.  Some key facts:

Total plane mass: 125 kg
Science payload mass: 12 kg
Total returned data: ~2Gbytes

Compared to previously proposed balloon missions (both the 2006 $1B Box study and the Titan Saturn System Mission (TSSM) proposal), this mission has some compromises.  The science payload is about half of what the balloons would have carried (see table below).  Some key instruments such as a mass spectrometer to study atmospheric composition and a radar sounder are not included in the AVIATR proposal.  The TSSM balloon mission would have returned far more data, but that was contingent on the presence of a flagship orbiter to relay data.  The data rate of the AVIATR mission appears to be similar to that of the $1B Box study balloon platform, which would have sent data directly to Earth. However, almost twice as much data would be returned by AVIATR because the balloon would spend half its time facing away from Earth when it would have been on the night side of Titan.

Instruments proposed for the AVIATR plane and the TSSM balloon platform

On the other hand, being able to actively manuever gives AVIATR some key advantages over a balloon.  When AVIATR reaches a target location, it can climb high and fly a grid pattern to take context images of the entire area.  Then it can drop down to ~3.5 km to take high resolution images of portions of the area.

To make the most use of the 2GB of data return, AVIATR would send thumbnail images back to Earth.  Scientists would then select the most interesting images for full transmission, and AVIATR would use data compression to make maximum use of the bandwidth.  A similar scheme was used for the Galileo mission, which had to deal with a similarly constrained data rate due to a malfunctioning antenna.

The cost of the AVIATR mission is described as either Discovery class (~$800M) or New Frontiers class (~$1.2B).  (These are fully burdened costs derived from dividing the proposed decadal budget for these programs by the number of expected missions.  The costs include the ~$450M and ~$650M, respectively, allocated to the principal investigator plus launch vehicle and presumably other overhead.)  The $1B Box study estimated the cost a standalone balloon mission at ~$1.4B using what appears to be similar accounting methods but in FY06 dollars.

Editorial Thoughts: I do believe that we should continue the exploration of Titan and Enceladus in the coming decade.  Currently, the flagship mission slot is given to the Jupiter Europa Orbiter over the Titan Saturn System Mission (a decision I agree with, but one the Decadal Survey could overturn).  In my opinion, portions of the TSSM proposed mission should be flown: An Enceladus multi-flyby (and possible orbiter) mission that would also study Titan in a series of flybys, a Titan lake lander a la the proposed TIME mission, and either a Titan balloon or airplane mission.  There are indications that all of these components individually could be in the Discovery to New Frontier mission class.  Ideally, this would be an international effort with more than one space agency contributing the mission elements. I would like to see the balloon or plane carried to Titan by the Enceladus Saturn orbiter that would also act as a data relay and enable substantially more than 2GB of data to be returned.

If a balloon or plane mission were to be flown, I'd prefer the plane mission.  The plane could better study the surface by flying to chosen locations of high interest rather than depending on the fate of wind direction.  To partially make up for the limited atmospheric instruments in the plane mission, the Titan lake lander could perform atmospheric chemistry measurements during its descent.

Thursday, May 20, 2010

Two Good Articles to Read

Two good articles have been published in the last few days.  The first, from Air & Space magazine describes the proposed AVIATR Titan plane proposal.  The article provides more background on this concept than I've seen before and provides images of the current design. (See this blog entry for a description and pictures of previous designs.)  Unlike proposals for Mars airplanes, the AVIATR design doesn't require folded wings. Deployment following entry into Titan's atmosphere is gentle.  “The clamshell’s heat-resistant bottom drops away, AVIATR is released, and the airplane noses into the airstream and levels off. Its speed at deployment is leisurely—a mere 25 mph. (A Mars airplane, by contrast, separates from its parachute at nearly the speed of sound, then has to unfold and begin flying in a matter of seconds. Lemke calls it the “death plunge.”)”  You can check out the article at http://www.airspacemag.com/space-exploration/Titan-Air-.html#

The second article from the journal Nature describes the hope that the Falcon 9 launcher nearing it’s first test flight will fill a critical hole in NASA's plans.  As I discussed in a previous blog entry, NASA will soon lose its workhorse moderate cost Delta II launcher.  As the article states, “’We're almost reaching the stage of desperation for launch vehicles,’ says Jack Burns, a space scientist at the University of Colorado at Boulder and a member of NASA's science advisory committee. NASA science chief Edward Weiler adds, ‘If there is no replacement ever for the Delta II, that would take away a critical capability.’ He hopes that in three or four years the Falcon 9, developed by SpaceX of Hawthorne, California, will emerge as a low-cost replacement. ‘Very much hoping, I might add.’”  The article is posted at http://www.nature.com/news/2010/100518/full/465276a.html

Correction: I should have also pointed out that the Nature article discusses  Orbital Sciences' Taurus II launcher which could fill the gap for small lunar and planetary missions.

Thursday, April 15, 2010

AVIATR poster

Mike Malaska has posted the poster used at two recent conferences for the AVIATR Titan airplane concept.  Click on the picture to go to his flickr page.


You can read an abstract on this Discovery mission proposal here

Saturday, March 27, 2010

Europa vs. Titan Redux?

The presentations at the February OPAG meeting held statements that the Europa versus Titan decision may come back up for review. Last year, two teams competed to be selected for the next NASA Flagship mission and for a place in ESA's next large mission competition.  The review teams concluded that the science from either mission would be equally good, but that a decade of technology development made the Europa mission much more ready for development than the Titan mission.  A NASA Europa mission got the nod and an ESA Ganymede orbiter won a spot to compete against two astronomy missions (with the ESA decision to come next year).  Both space agencies promised to fund advanced mission planning and technology development to make the Titan mission ready for its own start later in the decade.  [Editorial note: The Survey could decide not to prioritize missions to either Europa or Titan, but I wouldn't take a bet on that outcome.]

Now, that decision on the American side is up for review as part of the Decadal Survey.  NASA has made it clear that it will take its priorities for planetary missions in the coming decade from the Survey's priorities.  Any mission that has not received a formal new start from Congress must be recommended by the Survey for NASA to procede.  That includes the Jupiter Europa orbiter.  


NASA's current budgets continue to fund the Jupiter-Europa for Phase A, which is the period of advanced development before final design, manufacture, and testing begin.  Funding beyond Phase A is contingent on the Decadal Survey making this mission a priority.  To do that, the Survey would have to deprioritize other elements in NASA's current roadmap.  At $3.2B, there simply isn't room in the budget for this mission and the current Mars program and the New Frontiers and Discovery programs (see here for analysis of latest NASA budget proposal).

At the same time, the proponents of Titan as the choice for outer planet exploration are working to be making their voices heard.  One of them, Ralph Lorenz, presented at the meeting.  He showed that Titan has been to subject of many more scientific articles than has Europa over time. (To be fair, the Cassini-Huygens mission has returned far more data on that moon than the crippled Galileo spacecraft did for Europa.)  He also complained that promised funding for advanced development of a future Titan mission has not been forthcoming.  As an example, he described how promised money to develop balloon technology for a Titan mission had gone instead to fund the Decadal Survey.

Cassini's continued exploration at Titan continues to build the case for returning to that world and to neighboring Enceladus.  The case also is being made that Titan could be home to exotic forms of life and one scientific paper has prioritized Titan ahead of Mars as the best place for astrobiological exploration in the solar system (Europa came in third).  Recent finds at Enceladus continue to build the case that that moon has an internal ocean that could host life.

Whether to return to Europa or Titan or both or neither in the coming decade looks to be one of the biggest decisions facing the Decadal Survey.


Editorial Thought
s: Europa-Jupiter and Titan-Enceladus-Saturn both are compelling targets for exploration.  Both destinations should be explored in the coming decade.  However, the radiation belts at Jupiter impose significant technical challenges to any mission that will meaningfully answer the question of whether Europa could be explored for life, either by finding a thin point in the ice to penetrate or by finding a location where recent eruptions have brought ocean material to the surface.  On the other hand, Titan-Enceladus-Saturn presents a relatively benign environment (if a bit chilly within the atmosphere of Titan), but the mission design and technology apparently aren't ready to fly for some of the most exciting mission concepts.

If the decision were up to me, I would commit to the $3.2B Europa-Jupiter mission and budget another $2B for Titan-Enceladus-Saturn, which might be expanded if other space agencies contributed.  I'd go ahead with the Jupiter Europa Orbiter as planned -- it's ready to go and the harsh environment at Europa doesn't favor cheap missions.  It would also do for the Jupiter system what Cassini is doing for the Saturn system and what Galileo with its crippled antenna couldn't.  Around $2B probably would fund a highly capable orbiter or a less capable orbiter (perhaps similar in scale to the proposed Io Volcano Observer)  and a Titan in-situ probe such as a lake lander.  



An alternative strategy would be to commit ~$3B to Titan-Enceladus-Saturn, perhaps for a combination of New Frontiers scale missions.  Perhaps a Saturn orbiter could execute a number of flybys of Titan and Enceladus with  instruments tuned to fill gaps in Cassini's investigations.  The orbiter could also act as a relay for one or two in situ Titan craft, perhaps the Titan Mare Explorer and the aerial AVIATR.  The Europa-Jupiter mission would then be constrained to a $2B mission.  Within that budget, a capable craft could perform a number of flybys of all the Galilean moons, study Jupiter from afar, and perhaps orbit Europe for weeks instead of the months planned for the Jupiter-Europa Orbiter.  However, the orbiter missions under investigation by the Decadal Survey do not currently include alternatives to the Flagship, ~ $3B, Europa Jupiter System Mission and the Titan Saturn System Mission for exploring those two moons.  The Survey is looking at a number of mission concepts to explore Enceladus, a Titan Lake lander, a Ganymede observer, and an Io observer.

Either of these plans could leave ~$5B for Mars exploration, which would fund the Mars Trace Gas orbiter and the 2018  ExoMars/Max-C mission and leave ~$2.5B for other Mars missions, presumably down payment on a sample return.  In this scheme, lunar, inner planet, and small body exploration would have to share the remaining ~$2B, which would fund perhaps a Discovery mission and a New Frontiers mission.

Baring breaking news on future planetary exploration, the next two blog entries will look at the planning for the science that the Jupiter Europa Orbiter could do for Jupiter and the Galilean moons other than Europa.

Resources:



Updates on NASA outer planets program and status of Jupiter Europa Orbiter funding from Feburary OPAG meeting
Ralph Lorenz's OPAG Presentation on status of Titan mission planning

Space News article on possibility of life on Titan http://www.space.com/scienceastronomy/titan-water-life-am-100323.html


Paper prioritizing Titan for astrobiology missions, The Search for Alien Life in Our Solar System: Strategies and Priorities


Tuesday, February 16, 2010

AVIATR: Titan Plane Proposal


Off and on for the last 25 years or so, aircraft have been proposed to explore Mars.  Their advantage has been that they could study long swaths of the surface from elevations of just a few kilometers (compared to hundreds of kilometers for a low orbiter).  Their disadvantage has been that Mars is hard to fly in -- the air at the surface is thin -- limited communications bandwidth, and power/fuel for only a few hours of flight.  The last serious proposal for a Mars aerobot was the ARES proposal for a Scout mission competition.  The mission wasn't selected, and the role of high resolution imaging has moved to orbiters with extremely powerful cameras (really small telescopes), long lifespans, and high data rates to Earth.  (However, no platform has been flown to carry out an plane or balloon's role for in situ atmospheric studies or detailed subsurface mapping with ground penetrating radar.)

ARES plane design.  Wingspan would have been 6.25 m, requiring three folds to fit within the aeroshell.  From http://www.engr.uky.edu/~bigblue/I2Event/NASA_ARES_REBrief.pdf


Now a proposal has been put forth for a Titan airplane as an alternative to the frequently discussed Titan balloon mission.  Where Mars is hard to fly, Titan would be easy: Low gravity and a dense atmosphere make flight "over 1000 times easier at Titan than at Mars and more than 20 times easier than on Earth". (LPI abstract)"  [I'm no fluid dynamicist, but flying in the dense atmosphere of Titan may be more akin to moving through water than flying as we know it in the comparatively thin fluid known as our atmosphere.]  Essentially perpetual power could be provided by a plutonium-powered ASRG.

Up until this proposal, it has been presumed that in situ exploration within Titan's atmosphere would be conducted with a hot air balloon powered by the much heavier MMRTG plutonium power generators.  While the MMRTG's contain more plutonium and produce more waste heat (useful for heating gases for a hot air balloon), the power-to-weight ratio of these generators was too low for use with an airplane.  The much lighter ASRG units are a "game-changer" enabling powered flight by a propeller driven plane.


 Schematic of proposed Titan plane.  Wingspan would be approximately half that of the ARES plane, allowing easier fit within the aeroshell.  This may be an earlier concept since the antenna appears to be placed outside the aeroshell.  From http://www.info.uidaho.edu/documents/2010%2001%2025%20Barnes.pdf?pid=118467&doc=1

Either a balloon or an airplane platform would be a key element in exploring Titan.  The hazy atmosphere of this moon makes it difficult to image the surface (although some near-infrared spectral windows exist).  The depth of the atmosphere makes it impossible for an orbiter to hug this world the way that Mars orbiters can.  At Titan, an orbiter would maintain a distance of 1500 km compared to the 300-400 km orbits at Mars.  Within the atmosphere, high resolution images and radar soundings of the subsurface can be obtained.  An in situ probe can also make detailed atmospheric composition and weather measurements impossible from an orbiter.

An airplane would have a number of advantages over a balloon:
  • The plane can remain constantly on the sunlit side of the moon and thus in direct communication with the Earth.  (At the equator, the plane would have to average just 13-14 km per hour to remain on the sunlit hemisphere.)
  • While a balloon's flight would be at the whim of the winds, a plane could be directed to specific regions for study.
  • The plane's design and software could make use of the extensive heritage of design for unmanned aereial vehicles (UAVs) used by the military on Earth.  For a platform that will have to operate autonomously for much of the time because of the time delay for commands from Earth, this is a key heritage.
The plane that has been proposed would be small, around 120 kg, about the same weight as the gondola of the proposed Titan Saturn System Mission Montgolfere.  The published summaries of the plane proposal do not include a list of instruments and talk only about acquiring images.  However, the TSSM planning documents provide a list of potential instruments for the balloon mission that would also be valuable on an airplane (TSSM In Situ Elements pages 53-54):
  • Visible imaging system (2 kg) with three wide angle and one narrow angle camera
  • Infrared spectrometer (3 kg) for measuring surface composition and temperature and cloud properties
  • Chemical analyzer (6 kg) to measure atmospheric composition through mass spectrometry
  • Atmospheric structure and meteorological package (1 kg)
  • Electrical Environment package (1 kg) to study the coupling of the atmosphere and ionosphere with the magnetosphere of Saturn
  • Magnetometer (0.5 kg)
  • Radar sounder (8 kg) to to study the subsurface structure to > 350 m depth
In general, planetary probes can carry instruments weighing between 10-20% of their weight. Given this limitation, the plane could carry half to the full list compliment of this instrument list.  However, space limitations might further limit the instrument compliment. 

The proposers are pitching the mission as a stand alone Discovery or New Frontiers mission that would fly without a supporting Saturn orbiter for communications relay.  They point out that the scientific results would be limited by the bandwidth of the antenna carried within the plane's nose.  They propose that the plane would download thumbnail of the data gathered, with scientists on Earth deciding which subsets of full full data sets would be returned.

The authors of the abstract describing the Titan airplane provide a compelling case for the mission.  The plane "allows directed exploration of Titan’s sand dunes, mountains, craters, channels, and lakes, features of primary geologic interest as evidenced by the number of journal articles on the topics over the past several years. Subsequent imaging can search for changes. The airplane can fly predesigned routes in order to build up large context mosaics of areas of interest, and then swoop down to low altitude to acquire high-resolution images at 30-cm spatial sampling similar to that of HiRISE at Mars. The elevation flexibility of the airplane allows us to acquire atmospheric profiles as a function of altitude at any desired location."  (LPI abstract)

ARES full and half sized test vehicles.  The proposed Titan AVIATR plane would be closer in size to the half sized ARES test vehicle.  From http://marsairplane.larc.nasa.gov/platform.html

Editorial Thoughts:  This is a bold and exciting proposal.  It could significantly enhance our understanding of Titan by providing high resolution studies of the surface and atmosphere gathered over months to years.  The ability to send the plane to specific regions of Titan to fly over the Xanadu highlands, cross the boundary from land to sea, or explore the river channels is absolutely compelling.  The ARES proposal included a video camera (along with more scientifically oriented imagers) that would have allowed armchair explorers on Earth to ride along. 

Because the mission builds upon the heritage of UAVs and Mars plane designs, the technology to implement the mission may be mature.  Whether the technology is mature enough for flight is out of my expertise -- who but aerospace engineers could have judged that the proposed designs for Titan Montgolfere were too immature to fly?  There is also the issue of plutonium supply for this mission.  Right now, NASA would have enough for one Discovery mission and the Jupiter Europa Orbiter if Russia honors its contracts, which it currently is saying that it won't.

I am coming to personally favor a set of missions to the Saturn in the upcoming decade.  A Titan atmospheric probe/lake lander would explore the chemistry of both fluid systems.  A New Frontiers-class Titan-Enceladus Saturn orbiter would provide further studies with optimized instruments from a number of flybys of both moons.  And either a balloon or plane (depending on technology maturity) would explore Titan from within the atmosphere.  Preferably, the last mission would fly in conjunction with or after the Saturn orbiter so that the latter could provide a communications relay.

Unfortunately, the solar system is full of compelling targets.  The series of modest Saturn system missions outlined above would total $3-4B if the lander and plane can fit within Discovery budgets and the orbiter within a New Frontiers budget.  Add $3.2B for a Jupiter-Europa orbiter and $3-4B for Mars exploration, and you've spent most of NASA's projected budget of ~$13B for the coming decade and done nothing for exploring Venus, the moon, asteroids, or comets.. The Decadal Survey will have tough choices between excellent missions.

Resources

LPI Abstract: AVIATR: Aerial Vehicle for In-situ and Airborne Titan Reconnaissance

ARES Mars Scout Proposal  The first video at http://marsairplane.larc.nasa.gov/multimedia.html#videos is nice overview of the ARES proposal.

Titan In Situ Elements (TSSM) report

Enceladus New Frontiers Mission Concept

Titan Science from a Saturn Orbiter

Wednesday, October 14, 2009

Titan Mare Probe

Space.com has an article on the proposed Titan Mare Explorer that would float a probe on one of that moon's seas. I believe that all the material in the article has been presented in this blog, but it makes a nice read. http://www.space.com/businesstechnology/091014-titan-boat-mission.html

Wednesday, September 16, 2009

Dive! Dive! -- Titan Submersible

In the past couple of weeks, I've posted three entries on the proposed Titan Mare Explorer that would float a probe for months on the surface of a Titan lake.

I learned yesterday from a Decadal Survey white paper that Titan lake floaters are small dreams. A white paper that apparently is based on a SwRI study proposes a Titan lake submersible. Details on the implementation are sketchy, but it appears that the probe would first float on the surface and then fill ballast tanks (or alternatively detach from a flotation device) to sink to the lake bottom. It's not clear whether the ballast tanks could be blown to resurface. There's also no information on how the craft would communicate to Earth once below the surface. Would the lake liquids be transparent to radio waves or would the craft periodically resurface?

The white paper includes the most succinct summary of why chemical measurements of Titan's lakes are a high priority: "the mixing ratios of minor constituents (hydrocarbons, nitriles, noble gases) dissolved in the ethane-methane fluid of Titan’s lakes are expected to be higher than in the atmosphere, enabling spectrometric measurements of significantly higher sensitivity than were achievable with the Huygens GCMS or the Cassini INMS. Measurements of the dissolved species will provide information needed to better constrain models of the formation and evolution of Titan and its atmosphere." In addition, "The relative deficiency of Titan’s atmosphere in oxygen gives rise to the question whether prebiotic organic chemistry at Titan (1) is terrestrial in nature, occurring in cryovolcanic ammonia-water flows or in melt pools resulting from impacts, or (2) represents an altogether different chemistry, “where ammonia substitutes for water, and Nchemical groups substitute for O-chemical groups” [Raulin and Owen, 2002, p.383; Raulin, 2008b]. With its hydrocarbon lakes and ammonia-water cryomagma, Titan affords a unique laboratory for the investigation of alternative—“weird”—biochemical processes involving nonwater polar solvents (ammonia) or nonpolar solvents (hydrocarbons) [cf. NRC, 2007]."

Submersion through the lake depth to the bottom would allow the examination of changes in pressure, temperature, and composition along the descent profile. The paper mentions possible sampling of the lake bottom sediments. The paper also talks about the measurement of lake tides from the bottom (using upward viewing sonar).

In addition to studies below the surface, the white paper emphasizes the importance of studies at the surface to study Titan's hydrological (methane-ological?) cycle. Apparently the craft would spend considerable time on the surface.

The paper briefly mentions that it might be possible to build a dual probe that includes a submersible and a floater. It doesn't say which or both might include the RTG power source. (Retaining it on the floater for long-term meteorological and hydrological studies would seem more important to me; the submersible might be battery powered and relay its findings through the floater.)

Click on image for summary of SwRI concept study.

The paper emphasizes that this would be a New Frontiers (~$650M) class mission.

Editorial Thoughts: An intriguing idea. I suspect that the design problems are greater than suggested by the paper ("...no major technical drivers that must be overcome..."). Just the problem of keeping the craft warm in a dense, extremely cool fluid would seem a challenge to me. And might the craft's temperature (it has to be kept warm inside and that heat will leak out) cause problems?

Whatever the technical challenges, this is an intriguing idea that seems to be exploration at its best. Imagine having the descent camera return images from the bottom of an alien sea (okay, it will probably just be dull mud flats, but still...).

Note: There's also been a lively discussion of Titan lake probes here at Unmanned Spaceflight that you might want to check out.

Resources:

Titan Lake Probe white paper

SwRI Concept for a Titan Submersible


Abstract for a the Titan Mare Explorer

Thursday, September 10, 2009

Thoughts on Titan Mare Explorer

John R. passed along these thoughts (posted with his permission) in response to the blog posts about a proposed Titan Mare Explorer (TIME) (http://futureplanets.blogspot.com/2009/09/titan-mare-explorer-abstract.html and http://futureplanets.blogspot.com/2009/09/titan-mare-explorer-time.html).

Here's a link to a large image of a watery horizon on a cloudy day on Earth:

http://retiredeagle.files.wordpress.com/2009/01/dsc02585.jpg

Makes me think we might want to pass on the imagery.

The chemical analysis is a must, and sounding for depth is too easy not to do, but I seriously wonder the value of a single depth measurement. As I understand it, the weight of water ice under liquid methane would be fairly low in Titan's gravity, so I wonder if the lake bottom might be very heterogeneous, making a point measurement like that sort of arbitrary. A single altimetry track provided by radar, if some wavelength could penetrate the liquid, would be infinitely more useful.

Even the chemical analysis will leave us wondering about anisotropies. The Earth's oceans vary in salinity by a factor of about 1.5 from one location in open water to another. And here's an interesting map of salinity for Lake Pontchartrain.

http://pubs.usgs.gov/of/2002/of02-206/env-issues/images/pg160fig2.gif

All of which is just to flag, mindful of the Galileo Probe's experience at Jupiter, the risk of anisotropies and the impact that has on the value of collecting data. Clearly, the value is still there, and we'd love to have it in hand, but it undermines the meaningfulness of the data to some extent, as long as we're comparison-shopping billion-dollar missions.

Editorial Thoughts: These issues emphasize, in my mind, the value of TIME being able to make measurements over months, which its plutonium power source would allow. That would allow it to examine the surface conditions under varying weather conditions (assuming they vary meaningfully over a few months). If the winds or currents can push the lander (raft? boat?) over a meaningful transect of the surface, then there would be more chances to sample compositional heterogeneity. This would also be useful for depth sounding. I wonder if the probe could be designed so that the structure above the surface would be more likely to catch the wind?

Wednesday, September 2, 2009

Titan Mare Explorer (TiME)

As I've mentioned in past blog entries, NASA is funding a series of studies of Discovery missions that could make use of the newly developed ASRG plutonium power supplies. One of the most intriguing has been the Titan Mare Explorer (led by Ellen Stofan), which would put a probe on the surface of one of the lakes of Titan. Public information on the proposed mission has been scanty, but an abstract for the upcoming Division of Planetary Sciences meeting provides a few hints (and I'll add a couple of tidbits I've picked up).

From the abstract, "The scientific objectives of the mission are to: determine the chemistry of a Titan sea to constrain Titan’s methane cycle; determine the depth of a Titan sea; characterize physical properties of liquids; determine how the local meteorology over the seas ties to the global cycling of methane; and analyze the morphology of sea surfaces, and if possible, shorelines, in order to constrain the kinetics of liquids and better understand the origin and evolution of Titan lakes and seas."

I've heard through the grapevine that the instrument suite would be limited (as befits a ~$450M mission) to a mass spectrometer, a meteorology and physical properties experiment (probably several instruments in a package), and a descent and surface camera. This may compare favorably with the instrument package that was proposed for the lake lander in the Titan Saturn System Mission flagship proposal -- it's hard to tell without detailed listings of the proposed instruments. One key instrument that I haven't heard of for the proposed Discovery mission would be a gas chromatograph, which would enable detection of complex molecules. The TSSM lake lander had a combined mass spectrometer/gas chromatograph while I've heard of only a mass spectrometer for the proposed Discovery mission. It isn't clear if the gas chromatograph has been dropped, or just isn't listed.

The Discovery proposal calls for, as I understand it, six months of observations as the probe floats on the lake surface with a possible mission extension of several more months. Depending on how far the probe travels on the surface of the lake, this might allow depth measurements along a significant transect and might even bring the probe to a shore.

Editorial Thoughts: This is an exciting mission proposal. I'd love to see images from the surface of an alien ocean. The measurements of the lake composition would greatly advance our understanding of Titan chemistry.

However, there are some caveats to keep in mind. Data relay would be direct to Earth. Think of tens to hundreds of bits per second, most likely. We are unlikely to get great panoramas of photos. Think postage stamp images. Secondly, Titan is a cold place place (to put it mildly). Designing a probe that can reliably survive months on a Discovery budget may prove to be optimistic. Remember that one of the areas of technology development proposed to enable future Titan landers is technology to survive and operate in the frigid climate.

Still, I like this proposal, and hope that it is feasible in a Discovery budget.

Resources: Titan Mare Explorer abstract

Tuesday, August 25, 2009

Titan: A Thought Experiment

Given the tight budgets for planetary exploration, I worry that large flagship missions to the outer planets may never fly. The current strategy is to fly ~$3B flagship missions once a decade: first the Jupiter Europa orbiter (JEO), then a Titan Saturn orbiter, and then possibly at Europa lander (if JEO finds a location with interior materials at or near the surface that is safe to land at). At the moment, NASA's planetary program would have to forgo either the Mars program or the Discovery/New Frontiers programs to pay for a $3B flagship mission. (Alternately, NASA could give up portions of both programs, but the point is that $3B missions can't be afforded without giving up something else.) (This is a topic I've addressed before in this blog entry: http://futureplanets.blogspot.com/2009/05/what-next-for-titan.html.)

In this blog entry, I'd like to conduct a thought experiment to consider an alternative approach that might allow smaller scale missions to Titan could enable exploration of this fascinating world within tight budgets (and my expected lifespan). (See my thoughts on a possible alternative mission to Jupiter if the Jupiter Europa Orbiter cannot be afforded.)

I'd propose an on-going program of modest Titan missions carried out by multiple space agencies. A Titan lake lander could be a stand alone mission to provide compositional information. However, most other missions would require a data relay from an orbiter. NASA has made communications relay at Mars a priority (albeit also including scientific instruments on the orbiters) to enable high bandwidth communications with rovers. As a thought experiment, I would propose a similar strategy for Titan with each specific mission constrained to $650M to $1B. The key and first element would be a Saturn orbiter to provide communications relay and whatever scientific measurements would fit within the mission budget. (If affordable, my favorite would be a camera optimized to take advantage of the spectral windows in Titan's atmosphere for surface mapping.) The orbit initially might be chosen to optimize Titan flyby science and then later communications from Titan landers and balloons (although the same orbit might accomplish both). The orbiter might be a near twin of a Galilean icy moon observer to save costs. Given Cassini's long life, it would be reasonable to plan for a lifetime of a decade in orbit at Saturn. See this blog entry for examples of the science that a multi-flyby orbiter might be able to carry out.

After the relay is in place, several in situ missions could be flown:

A Titan lake lander for chemical measurements of the lake and atmosphere. While the main experiments might be battery powered and therefore short lived, a small plutonium power source would enable long-lived geophysical and meteorological measurements.
A geophysical network of landers for solid surface measurements powered by plutonium power sources to enable a lifetime of months to years.
One or more balloons to explore the atmosphere and make remote studies of the surface
Highly capable landers to carry out surface composition studies, possibly even with modest (to keep costs within reason; perhaps a couple of hundred meters) roving capabilities.

The Saturn orbiter would have to launch and arrive first. The order and timing of the subsequent missions could be dictated by launch opportunities and budgets. Breaking the missions up would allow multiple space agencies to contribute specific missions, spreading total costs among multiple nations.

A key difference between exploring Titan in small missions and doing the same at Mars is the flight times. Whereas Mars is months away, Titan is years. That alone would make each element more expensive. Data rates from the relay craft would be much lower than from Mars given the distance. This is one reason that the Saturn Titan orbiter is so expensive compared to Mars orbiters -- it needs lots of power to return high resolution mapping data. The modest Saturn orbiter in this thought experiment would have lower data rates than a flagship mission.

Closing Notes: Many really smart people have and will look at Titan exploration options. I'm under no illusion that I have ideas that are novel or that the ideas presented here are the best way to take advantage of limited budgets. I present them in the spirit of showing possibilities so that you can reach your own conclusions. As I did with the proposal for a Galilean Satellite observer mission, I'll publish thoughtful critiques of these ideas that are e-mailed to me at vkane56[at]hotmail.com.

Sunday, August 23, 2009

White Paper: Titan Exploration by Balloon

This blog entry continues to look at White Papers being prepared for the current Decadal Survey effort. In keeping with the theme of previous post on a proposal for a Titan network mission, this entry looks at the case for exploration of Titan by balloon. (Future in situ balloon exploration of Titan’s atmosphere and surface.)

Balloon missions to Titan have been extensively studied as part of the Billion Dollar Box study and the Titan Saturn System Mission analyses and proposals. This white paper provides a good summary of the scientific rational and engineering options for a balloon mission. I did not see anything, however, that struck me as new.

Titan is the best atmosphere in the solar system for ballooning. The atmosphere is cold and dense, making a hot air montgolfiere balloon simple and providing a long descent time to inflate the balloon. The sun is far away, meaning that little solar heat arrives at Titan, reducing the diurnal heating of the balloon and the subsequent stress on the balloon material. However, a number of technical issues have been identified that require further work before a mission could be flown. These include balloon deployment and inflation and packaging of the balloon and it radioactive power source. These issues are being worked with a goal to achieve flight readiness by 2015. The goal is a system that can circumnavigate Titan at least once (3 to 6 months) but that might have a lifetime of years.

The white paper lists a number of investigation firsts that would be enabled by a balloon carrying a sophisticated (i.e., large) payload:

"1. First analysis of the detailed sedimentary record of organic deposits and crustal ice geology on Titan, including the search for porous environments (“caverns measureless to man”) hinted at by Cassini on Xanadu.
2. Direct test through in situ meteorological measurements of whether the large lakes and seas control the global methane humidity, which is key to the methane cycle.
3. First in situ sampling of the winter polar environment on Titan, a region expected to be vastly different from the equatorial atmosphere explored by Huygens.
4. Compositional mapping of the surface at scales sufficient to identify materials deposited by fluvial, aeolian, tectonic, impact, and/or cryovolcanic processes.
5. First search for a permanent magnetic field unimpeded by Titan's ionosphere.
6. First direct search for the subsurface water ocean suggested by Cassini.
7. First direct, prolonged exploration of Titan’s complex lower-atmosphere winds.
8. Exploration of the complex organic chemistry in the lower atmosphere and surface liquid reservoirs discovered at high latitudes by Cassini."

The paper lists the one major problem with a Titan balloon mission. Imaging of the surface with cameras and spectrometers would require a relay craft in orbit around Saturn or Titan. (Chemical analyses of the atmosphere, atmospheric structure (e.g., pressure) measurements could probably be acheived with direct to Earth communications. Perhaps even ice penetrating radar measurements could be taken without a relay orbiter; I'm not sure how much data this instrument would generate.) The white paper assumes a highly capable orbiter similar to the Titan Saturn orbiter that would cost approximately $3B. As long as a balloon mission is tied to an expensive flagship mission, I don't believe this mission will arrive at Titan until the 2030s. In the next blog entry, I'll do a thought experiment about an alternative approach.

Friday, August 21, 2009

White Paper: Titan Geophysical Network

This blog entry will begin a series of summaries of Decadal Survey White Papers. These position papers are submitted by members of the planetary research community to make the case to prioritize specific lines of inquiry, measurements, and missions. Because the papers are meant to be read by a wide audience, they generally are not too technical on either the science or engineering sides. This makes them readable by interested members of the general public such as myself and probably most of the readers of this blog. The papers are also short. The papers are limited to seven pages and 12 point font. All papers are due by September 15, meaning that there will soon be a flood of publication to the White Paper website. Drafts of a number of papers have been posted, and I'll begin summarizing these.

A couple of notes, though. I cannot publish summaries in anything approaching real time (the penalties of a family and career). You can probably expect that I will still be writing summaries for the next several months. Nor am I likely to read and summarize all the papers -- there is likely to simply be too many. However, all the White Papers are available at this website, so you can read the ones of greatest interest to you.

I'll start this series with a White Paper written by Ralph Lorenz (with a number of co-authors). Lorenz is a much published scientist who focuses on Titan and also has led or participated in a number of task forces exploring mission options for future Titan exploration. He has published a couple of books on Titan for the general public. Ralph is also a good guy to share a beer with at a scientific conference.

Lorenz's paper is, "The Case for a Titan Geophysical Network Mission." The goal of the paper is to have the Decadal Survey prioritize this mission high enough that it would make the list of potential missions for a future New Frontiers ($650M) class mission. A second goal is to make the development of small plutonium powered energy sources a priority. (NASA is considering developing such a power source to enable small probes to a number of solar system targets.)

This proposal is one of a number of proposals to establish long-lived (at least months, preferably years) networks of fairly small landers on a moon or planet. A number of fields of study such as meteorology, seismology, and rotational state require measurements from multiple locations on a surface. This paper lists several areas of study that could be advanced with simple Titan landers:

  • Measure near-surface meteorology for both short-term changes, medium-term changes from the atmospheric gravitational tide as Titan orbits Saturn, and potentially long-term changes with the passing of the seasons
  • Variations in Saturn's magnetic field on the surface of Titan to explore the properties of the water-ammonia ocean beneath Titan's crust
  • Track changes in Titan's rotation and tilt to explore the interior structure
  • Possibly make seismic measurements (which would require a relay orbiter)

The paper points out that the basic measurements could be made with sensors common in many high end watches: "a pressure sensor, a magnetometer, a light sensor, and a thermometer." If budgets allow, the landers could also carry a tiltmeter to study tidal deformation of the crust, a wind instrument, a seismometer, a communications system that allows precise doppler tracking, and a wind measurement instrument. A descent camera could take images of the landing site.

The paper is short on specifics, leaving the detailed definition to the proposers of an actual New Frontiers mission. Instrument mass could be as low 1.5 kg to 20 kg. The mission would fly four probes to Saturn on a carrier craft that drop the probes off without entering Saturn or Titan orbit. Communications would be direct to Earth, which would limit the bandwith to as little as 1 bit per second.